Active implantable medical devices generally include a housing, which is often called “the generator”, that is mechanically and electrically connected to one or more “leads” that have electrodes that in turn come into contact with the tissues to which it is desirable to apply electrical pulses and/or to collect an electrical signal of the patient's myocardium, nerve, or muscle.
Standardized connection systems have been used for years to ensure an interchangeability of the leads and generators produced by different manufacturers. Thus, the standards called “IS-1” and “IS-4” define a number of dimensional and electrical characteristics for the leads to be connected to the generator. For defibrillation or cardioversion leads, wherein electrical stresses are more severe in view of the high energy passing from the generator to the lead, the “DF-1” and “DF-4” standards define the dimensional and electrical characteristics of the connection system.
The complexity of multi-polar leads, which already incorporate specific constraints in terms of the electrical energy associated with delivery of pacing or shock pulses, is enhanced by the development of multisite devices and intracardiac sensors, such as peak endocardial acceleration (PEA) sensors. This complexity leads, in terms of connectivity, to a proliferation of connection plugs, in addition to different standards depending on the plugs.
It is thus desirable to obtain a single plug that is subject to a single standard having a plurality of electrical contacts to simultaneously ensure connections to various terminals of the generator for all applicable energy levels, whether for the collection of depolarization signals, for the application of stimulation pulses or for the delivery of a defibrillation shock. In this context, a single “isodiametric” connection plug, namely a plug having a uniform cylindrical shape, designed to be inserted in a counterpart cavity of the generator, is known.
EP 1641084 A1 and its counterpart U.S. Pat. No. 7,175,478 (both assigned to Sorin CRM S.A.S. previously known as ELA Medical) describes one such isodiametric connection plug with the outer cylindrical surface having a stack of annular electrical contact zones, realized with alternating conductive cylindrical rings and insulating zones, the latter designed to electrically isolate the conductive rings. In addition, each electrical contact in the cavity of the generator must be isolated from the other contacts and from the environment outside the cavity by suitable seals. Originally placed on the lead, these joints are now placed in the cavity because of the fact, more particularly for defibrillation leads, high voltages are applied to the contact elements. It is therefore essential that the connecting pins of the multipolar leads are dimensionally stable over time and comply, with precise tolerances, with the geometric description of the imposed standards. These requirements help ensure that the electrical contact zones and insulating zones coincide with the corresponding zones of the cavities of the generators, when inserting the connector plugs into the cavities, as well as during the useful life of the active implantable medical device.
In this context, two key parameters must be taken into account, namely, on the one hand, the surface state of the electrical contact and insulating zones, and on the other hand, the coaxiality of the electrical contact and insulating zones along the connection plug. These parameters are indeed crucial for the quality of the electrical contact in the generator cavity and for sealing the system.
With these constraints, the difficulty of making a plug connector with a constant diameter along the entire length of the part and with multiple electrical contacts is increased, which in turn raises many manufacturing problems. In addition, the constraint of a small outer diameter (e.g., 3.2 mm according to ISO 27186) limits the design possibilities, so that the impact of complying with tight tolerances that are needed for industrial production can be considerable in terms of time and cost.
In this context, the connection plug described in EP 1641084 A1 and U.S. Pat. No. 7,175,478 mentioned above is not entirely satisfactory, because it does not guarantee a perfect coaxiality of the different zones. Indeed, in this prior art plug, the electrical contact zones and insulating zones are defined by cylindrical elementary parts the axial and angular alignment of which is obtained by longitudinal rods fitted in bores formed in each counterpart section of elementary parts. However, the minimum functional space between the pins and bores to allow stacking of the elementary parts leads to a lack of concentricity of the assembly, detrimental to the electrical contact and sealing of the connection plug inside the generator cavity.
U.S. Patent Publication No. 2005/221671 A1 proposes a plug for electrical connection of a multipolar lead for an active implantable medical device, said plug having a cylindrical outer surface including a plurality of annular electrical contact zones axially distributed and formed of conductive cylindrical rings, the electrical contact zones being alternately separated by a plurality of intercalary insulating cylindrical zones. The plug connector further includes an insulating monobloc core, a piece having a generally cylindrical shape and a plurality of coaxial centering side cylindrical surfaces, with a conductive ring being placed on at least one centering side surface. The desired coaxiality of the conductive rings directly results from the centering side surfaces formed during the manufacture of the monobloc core piece. The fact that there is a unique piece for the central core, so with no functional clearance, ensures the long term stability of the coaxial rings.
However, the described structure requires welding the wire “blind” in a through-hole of the conductive ring, without the possibility of any visual inspection of the weld integrity. The problem of correct positioning of the different rings (i.e., the conductive rings provided with their welded wire and the insulating rings) during the assembly of the plug also remains, while satisfying the constraints of longitudinal alignment and of centering of the rings (namely, for an optimum, and desired perfect, coaxiality of the electrical contact and insulating zones), with a sufficient reproducibility and reliability, without significant increase in production costs and with simple parts and simple manufacturing and control processes, as appropriate for an industrial solution with profitability and efficiency for production in large quantities.